The invention relates to a laminated composite containing a layer arrangement and an electronic substrate and also to a circuit arrangement containing a laminated composite. The invention further relates to a method for forming a laminated composite.
Power electronics are used in many technical fields. The use of power electronics is unavoidable particularly in electrical or electronic devices in which high currents flow. The current intensities which are required in power electronics lead to thermal loading of the electrical or electronic components which are present. Further thermal loading is caused by the use of such electrical or electronic devices at places of operation having a temperature which is significantly above room temperature and which may also change continually. Examples which may be mentioned in this respect are control devices in the automotive sector which are arranged directly in the engine compartment.
In particular, many connections between power semiconductors or integrated circuits (ICs) among one another and also to carrier substrates are even today subject to long-term thermal loading of up to 175 degrees Celsius.
Electrical or electronic components are usually joined—for example to a carrier substrate—by a joining layer. Solder joins are known as a joining layer of this type.
Use is usually made of soft solders based on tin-silver or tin-silver-copper alloys. However, particularly at use temperatures close to the melting temperature, such joining layers display a decrease in electrical and mechanical properties, which can lead to failure of the assembly.
Lead-containing solder joins can be used at higher use temperatures than soft solder joins. However, lead-containing solder joins are greatly restricted in respect of their permissible industrial applications by legal obligations for reasons of environmental protection.
An alternative for use at elevated or high temperatures, in particular above 200 degrees Celsius, is lead-free hard solders. Lead-free hard solders generally have a melting point which is higher than 200° C. However, when hard solder is used for forming a joining layer, only few electrical or electronic components which can withstand the high temperatures during melting of the hard solders come into question as join partners.
One solution is low-temperature joining technology (LTJ), in which silver-containing sintered joins can be produced even at significantly lower temperatures than the melting temperature. Here, a paste containing chemically stabilized silver particles and/or silver compounds is used instead of a solder. Under the sintering conditions, in particular at elevated temperature and applied pressure, the stabilizing constituents are burnt out and/or the silver compounds are decomposed so that the silver particles or liberated silver atoms come into direct contact with one another and with the material of the join partners. A join which is stable at high temperatures can be formed by interdiffusion and/or diffusion even at significantly lower temperatures than the melting temperature. However, when such sintered joins are subjected to temperature changes, thermomechanical stresses and even cracking can occur in semiconductor components or even in the carrier substrate.
DE 10 2009 002 065 A1 describes a solder which comprises a soft solder with a melting point of less than 450° C., in which a number of particles formed from an intermetallic phase or coated with an intermetallic phase are embedded. The solder can areally join a metalized ceramic substrate of a power semiconductor module to a base plate. To produce the solder join between the base plate and the ceramic substrate, the solder is heated to a temperature of at least 330° C.